A working range working range of an imaging based barcode reader is limited by several things including image sensor resolution, depth of focus of the optical system, and noise generated within the image sensor. Out of these factors, image sensor resolution can often be a limitation that cannot be easily overcome. This can be particularly prevalent when reading high density barcodes (barcodes with relatively small bars or spaces). The problem stems from the fact that the field of view of the sensor expands as distance from the reader is increased, spreading the pixels across a larger and larger area, reducing the number of pixels available to resolve small features, such as the narrow elements in a high-density barcode. Eventually, the small elements can't be adequately resolved, and the barcode can no longer be decoded.
This situation can be partially resolved by using an imaging sensor with more pixels. However, there are tradeoffs. Specifically, sensors with higher pixel count cost more, often use more power, and make higher demands on the decode microprocessor because there is more data to analyze. Another feature that can help is using optics that provide a field of view that doesn't grow as fast with distance. This results in a slower rate of degradation of resolution as distance increases. The tradeoff with this approach, though, is that the field of view close to the reader can be too small to read common barcodes. This is a problem since users typically hold barcodes relatively close to the reader, and have become accustomed to the reader working when they do so. If the field of view is too small to cover the barcode at the distance at which it is positioned, the reader won't be able to read it and the user may not realize why. To make matters worse, it seems intuitive to many reader operators that if a barcode can't read, it should be moved even closer to the reader, where the user expects the reader should be able to “see” the barcode better. This, however, makes the situation even worse.
Accordingly, there continues to be a need for improved barcode reader designs that allow for both short and long-range operation while maintaining relatively low cost and complexity.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.